I always knew them as "punt guns" which were mounted on the bow of a sneak boat.
In the United States, this practice depleted stocks of wild waterfowl and by the 1860s most states had banned the practice. The Lacey Act of 1900 banned the transport of wild game across state lines, and the practice of market hunting was outlawed by a series of federal laws in 1918.
I know for sure that this practice continued around some of the Chesapeake Bay islands long past 1918. They would run these boats at night as well as in the day light. Ducks tend to gang up in a "float" at night so the take was tremendous.
One of the problems these guys had was the muzzle flash would give them away to the federal boys.
"A pessimist sees the difficulty in every opportunity, an optimist sees the opportunity in every difficulty” ---Sir Winston Churchill
"Political extremism involves two prime ingredients: an excessively simple diagnosis of the world's ills, and a conviction that there are identifiable villains back of it all." ---John W. Gardner
“You can’t go back and change the beginning, but you can start where you are and change the ending.” ---C. S. Lewis